Methylation of Nicotinamide in Vitamin B12- and Vitamin B6-Deficient Rats

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Abstract
The effect of vitamin B12 deficiency on methylation, as indicated by the urinary excretion of methylnicotinamide following the administration of nicotinamide, was studied. It was found in male and female rats that dietary deprivation of this vitamin brought about a decrease in methylation. This effect is not due to nonphysiologic causes since pair-fed animals from both deficient and treated groups, as well as female rats in these two groups, exhibited a significant difference in excretion. Furthermore, vitamin B6 deficiency does not bring about such a difference. However, if vitamin B6 deficiency were prolonged, vitamin B12 serum level of these vitamin B6-deprived animals was reduced. Only then did a decrease in methylation occur. From these studies, it was concluded that vitamin B12 deficiency by dietary deprivation or by poor absorption of this vitamin decreases the urinary excretion of MNA.